Here's what I figure is in store for the human race in the future.
We will be facing a devastation the likes of which no one has ever seen; perhaps the annihilation of the whole planet. So, we will work and work and we will find what we THINK is faster-than-light drive, and we'll all pile on, to save our butts from certain destruction.
We'll travel briefly, and then we'll come upon a planet that looks habitable. Then we'll notice that it looks very familiar. Then we'll know we have gone into the past. NASA will cover it up so as not to inform the russkies that we have travelled through time, and we'll finish out our lives in the eras we know best.
That's the only way to explain how people who resemble my friends, but about 40 years older, show up every now and again.